1. Field of Invention
The present invention relates to a projector.
2. Description of Related Art
In recent years, attention has been focused on a projector (namely, a liquid crystal projector) employing a reflection type liquid crystal device. In such a reflection type liquid crystal device, a structure, such as a transistor, for driving a liquid crystal is incorporated under a reflection mirror. Consequently, the pixel density of the device can be enhanced. Therefore, the reflection type liquid crystal device has an advantage in that a higher-resolution and clearer projection image can be realized, as compared with the case of using a transmission type liquid crystal device.
Further, there has been proposed the use of an integrator optical system or a polarization conversion illumination system in a projector employing an electro-optical device, such as a liquid crystal device, so as to realize a bright projection image, which is free from display unevenness, and to reduce the size of the entire projector (see Japanese Unexamined Patent Application Publication Nos. 8-34127 and 10-232430). In the integrator optical system, a light beam coming from a light source is divided by a light beam dividing optical element into a plurality of light beams to thereby form a plurality of light source images, which are regarded as pseudo light sources. Then, light beams from a plurality of light source images are superposed on a liquid crystal panel. Consequently, light beams having uniform intensity distribution can be obtained. Further, in the polarization conversion illumination system, the illumination light beam is first separated into a plurality of light beams and then undergo the polarization conversion. Then, the light beams are superposed on the liquid crystal device. Consequently, illumination light beams whose polarization directions are uniform can be obtained.
Thus, it is considered that a higher-resolution and brighter projection image, which is free from display unevenness, can be realized by the use of the integrator optical system or the polarization conversion illumination system in combination with the reflection type liquid crystal device that is employed in the projector.
In the case of using a reflection type liquid crystal device, which utilizes a polarization mode as a display mode, in a projector, generally, a polarization beam splitter for spatially separating light beams, which are respectively in different polarization states, is used. This beam splitter has polarization separation characteristics that largely depend on an incidence angle of a beam. Practically, the polarization separation characteristics of this beam splitter have incidence-angle dependency according to which the polarization separation performance extremely lowers when the incidence angle of light becomes larger in a plane perpendicular to a plane of incidence defined in such a way as to include a substantially center axis of incident light and a normal to the polarization separation film of the beam splitter. Further, in the integrator optical system and the polarization conversion illumination system, optical processes performed therein inevitably result in increase in the incidence angle.
Thus, in the case of using the combination of the integrator optical system and the polarization conversion illumination system in the projector that employs the reflection type liquid crystal device, the incidence angle of light impinging upon the polarization beam splitter is increased. Thus, such a projector has problems in that the polarization separation performance of the polarization beam splitter is degraded, and that the light utilization efficiency thereof is lowered.
The present invention is accomplished in view of at least the aforementioned problems. One object of the present invention is to provide a projector that can at least realize a bright projection image with high light utilization efficiency by using the combination of a reflection type liquid crystal device and an integrator system or a polarization conversion illumination system.
According to an exemplary embodiment of the present invention, there is provided a projector which may include: an illumination device including a light beam dividing optical element for dividing a light beam into a plurality of sub light beams and for forming a plurality of light source images from the plurality of sub light beams; an electro-optical device for modulating an illumination light beams emitted by the illumination device; a projection lens for projecting light beams modulated by the electro-optical device; and a polarization separation film for selecting a light beam of a predetermined polarization component included in the illumination light beam emit the selected light beam of the predetermined polarization component to the electro-optical device, and for selecting a light beam of a predetermined polarization component from the light beams modulated by the electro-optical device to emit the selected light beam of a predetermined polarization component to the projection lens. The light beam dividing optical element is a rod-like light guide having an incidence end surface, an exit end surface, and at least four reflective surfaces. Assuming that an incident plane is a plane defined by a center axis of the illumination light beam and a normal to the polarization separation film, that a direction parallel to the incident plane and perpendicular to the illumination optical axis is the X-direction and a direction perpendicular to the incident plane is the Y-direction, that a length of the incidence end surface in the X-direction is MX and a length of the incidence end surface in the Y-direction is MY, that placement intervals of the plurality of light source images in the X-direction is SX and placement intervals of the plurality of light source images in the Y-direction is SY, then the lengths MX and MY and the intervals SX and SY meet the following condition:
SY/SX less than MY/MX.
The polarization separation performance of a practical polarization separation film has large dependency on the incidence angle of each incident light beam. Especially, when the incidence angle of each of the light beams increases in the Y-direction that is perpendicular to the incident surface, the polarization separation performance is extremely degraded. However, the projector of this exemplary embodiment of the present invention satisfies the condition
SY/SX less than MY/MX.
Thus, a range of incidence angles in Y-direction of a light beam impinging on the incident surface can be narrowed. Consequently, the polarization separation performance of the polarization separation film can be enhanced. Thus, a bright projection image having a high contrast ratio can be realized.
Further, in the case that a color separation optical system for separating an illumination light beam from the illumination device into a plurality of color light beams is added to the constituent elements of this projector, and that a plurality of the electro-optical devices for modulating the color light beams separated by the color separation optical system are provided in this projector, a high-resolution color display can be realized.
Preferably, in the projector of this exemplary embodiment, the distance between a pair of the reflection surfaces opposed to each other in the Y-direction of the light guide gradually increases toward the exit end surface from the incidence end surface. With such a configuration, the placement interval in the Y-direction of a plurality of the light source can easily be decreased. Thus, a range of the incidence angle in Y-direction of a light beam impinging on the polarization separation surface can be narrowed. Moreover, the polarization separation performance of the polarization separation film can be enhanced. Furthermore, a space, in which a plurality of images of the light source are formed, can be reduced. Consequently, the area of the polarization separation film can be reduced. Reduction in the size and weight of the entire illumination device can be achieved.
Further, the projector may be adapted so that the distance between a pair of the reflection surfaces opposed to each other in the X-direction of the light guide gradually decreases toward the exit end surface from the incidence end surface. In this case, the state in which the light source images are formed can be more freely controlled. Thus, the light utilization efficiency of the entire optical system can be enhanced.
Moreover, preferably, in the projector of this exemplary embodiment, the shape of the exit end surface of the light guide is similar to the shape of a display area of the electro-optical device. Consequently, the illumination efficiency can be improved.
Incidentally, in the projector of this exemplary embodiment, it is sufficient that the rod-like light guide has at least two pairs of reflective surfaces opposed to each other in first and second directions, and that thus, the shape of a section of each of the light guide is a quadrangle or a polygon having more than four sides and more than four angles. For example, the shape of a section of the light guide may be an octagon or a dodecagon. However, it is preferable in view of the light utilization efficiency of the projector that the light beam dividing element has a square incidence end surface. Further, as long as an incident light beam is reflected by the reflective surface and then divided into a plurality of light beams whose exit angles with respect to the exit end surface differ from one another according to the reflecting positions and the number of times of reflections, the rod-like light guide may be formed as a lump of a light guiding material or may be shaped like a cylinder. In the case that the light beam dividing optical element is a solid rod made of a rod-like lump of a light guiding material, the surface of the light guiding member placed along the illumination optical axis is a total reflective surface. Thus, the incident light is reflected by the surface of the solid rod while the incident light is transmitted in the light guiding material from the incidence end surface to the exit end surface. On the other hand, in the case that the light beam dividing optical element is a hollow rod formed by shaping a member having a light reflective surface into a cylinder, incident light is reflected by the light reflective surface (desirably, a surface reflection face) placed along the illumination optical axis of the hollow rod while the incident light is transmitted in an air layer formed in the hollow rod from the incidence end surface to the exit end surface. The former light beam dividing optical element formed as a lump of a light guiding material can transmit the light beam by total reflection that causes almost no light loss. Thus, the transmission efficiency is high. Conversely, in the case of using the latter cylindrical light beam dividing optical element that has the reflection surface, a uniform illumination light beam even when the dimension of a portion between the incidence end surface and the exit end surface is set at a relative small value. Moreover, the manufacturing of the latter light beam dividing optical element can be performed more easily than that of the former light beam dividing optical element. The manufacturing cost of the illumination device having the latter light beam dividing optical element can be made to be lower than that of the illumination device having the former light beam dividing optical element.
According to another exemplary embodiment of the present invention, there is provided a projector which may include: an illumination device including a light beam dividing optical element for dividing a light beam into a plurality of sub light beams and for forming a plurality of light source images from the plurality of partial bundles of light beams; an electro-optical device for modulating an illumination light beam emitted by the illumination device, a projection lens for projecting light beams modulated by the electro-optical device device; and a polarization separation film for selecting a light beam of a predetermined polarization component included in the illumination light beam to emit the selected light beam of the predetermined polarization component to the electro-optical device, and for selecting a light beam of a predetermined polarization component from the light beams modulated by the electro-optical device to emit the selected light beam to the projection lens. The light beam dividing optical element is a lens array having a plurality of small lenses. Assuming that an incident plane is a plane defined by the center axis of the illumination light beam and a normal to the polarization separation film, that a direction parallel to the incident plane and perpendicular to the illumination optical axis is the X-direction and a direction perpendicular to the incident plane is the Y-direction, that a length of a contour of said small lens in the X-direction is MX and a length of the contour of the small lens in the Y-direction is MY, and that placement intervals of the light source images in the X direction is SX and placement intervals of the light source images in the Y direction is SY, then the lengths MX and MY and the intervals SX and SY meet the following condition:
SY/SX less than MY/MX.
Thus, even in the case of employing a lens array as the light beam dividing optical element, a range of the incidence angle in the Y-direction of a light beam impinging on the polarization separation film can be reduced, similarly as in the case of the projector of the previous exemplary embodiment. Consequently, the light utilization efficiency of the entire projector can be improved while the polarization separation performance of the polarization separation film is enhanced. Incidentally, the small lenses which form the lens array may be ordinary lenses, whose surfaces are formed as curved surfaces. Alternatively, a hologram lens which condenses light by holographic effects, or a diffractive lens which condenses light by diffraction may be employed as the small lens.
Further, in the case that a color separation optical system for separating an illumination light beam emitted by the illumination device into a plurality of color light beams is added to the constituent elements of this projector, and that a plurality of the electro-optical devices for modulating the color light beams separated by the color separation optical system are provided in this projector, a high-resolution color display can be realized.
Preferably, in the projector of this exemplary embodiment, the contour of the plurality of small lenses is similar to the shape of the display area of the electro-optical device. The images formed on the small lenses are superposed on the electro-optical device serving as an illumination area. Thus, the illumination efficiency can be enhanced by making the shape of the lens similar to the shape of the electro-optical device.
Moreover, in the projector of this exemplary embodiment, it is preferable that at least a part of a plurality of small lenses are decentered lenses. With such a configuration, an image of the light source can be formed at a position that is other than the physical center of each of the small lenses, which allows intervals at which light source images are formed to be controlled freely.
Furthermore, in the second projector, preferably, the illumination device has a reduction optical system for reducing a diameter of a light beam. With such a configuration, the diameter in Y-direction of an illumination light beam can be still further reduced. Thus, the polarization separation performance of the polarization separation film can be still further improved. Additionally, the necessity for setting the condensing characteristics of the plurality of small lenses is eliminated. Furthermore, the diameter of the entire light beam which illuminates the illumination area can be reduced. Thus, after modulated by the electro-optical devices (for instance, liquid crystal devices), the diameter of the entire light beam reaching the projection optical system can be reduced. Consequently, the projector of this exemplary embodiment has an advantage in that the light utilization efficiency of the projection optical system can be improved.
Needless to say, the projector may be configured so that the diameter in the X-direction of the illumination light beam is simultaneously reduced by the reduction optical system. Such a configuration is easy to employ in the case of using a light source that is close to a point light source.
Incidentally, such a reduction optical system can easily be realized by an afocal optical system. Further, in this reduction optical system, a cylindrical lens can be used as the lens of the afocal optical system in the case that only the dimension in the Y-direction is reduced.
According to another exemplary embodiment of the present invention, there is provided a third projector which may include: an illumination device for dividing a light beam into a plurality of sub light beams and for forming a plurality of light source images from the plurality of sub light beams; an electro-optical device for modulating an illumination light beam emitted by the illumination device; a projection lens for projecting a light beam modulated by the electro-optical device; and a polarization separation film for selecting a light beam of a predetermined polarization component included in the illumination light beam to emit the selected light beam of the predetermined polarization component to the electro-optical device, and for selecting a light beam of a predetermined polarization component from the light beams modulated by the electro-optical device to emit the selected light beam to said projection lens. The illumination device has a reduction optical system for reducing a diameter of a light beam. Assuming that an incident plane is a plane defined by the center axis of the illumination light beam and a normal to the polarization separation film, and that a direction parallel to the incident plane and perpendicular to the illumination optical axis is the X-direction and the direction perpendicular to the incident plane is the Y-direction, then a rate of reduction in the diameter of the light beam in the Y-direction by the reduction optical system is larger than a rate of reduction in the diameter thereof in the X-direction.
Thus, even in the case of the configuration in which the reduction optical system for reducing the diameter of the light beam is provided between the illumination device and the polarization separation film to thereby make the rate of reduction in the diameter of the light beam in the Y-direction of the bundle of light beams larger than the rate of reduction in the diameter thereof in the X-direction, the range of the incidence angle of the light beam impinging on the polarization separation film can be reduced in the Y-direction, similarly as in the case of the projector of the first exemplary embodiment. Consequently, the light utilization efficiency of the entire projector can be improved while the polarization separation performance of the polarization separation film is enhanced. Further, in this case, the range of the incidence angles of the light beam impinging upon the polarization separation film can be reduced in the Y-direction without designing the illumination device so that
SY/SX less than MY/MX
holds, similarly as in the case of the projectors or the previous exemplary embodiments. Thus, the configuration of the illumination device can be simplified. Incidentally, a rod-like light guide may be used as the light beam dividing element, similarly as in the case of the projector of the first exemplary embodiment. Alternatively, a lens array may be used as the light beam dividing element, similarly as in the case of the projector of the second exemplary embodiment.
Further, in the case that a color separation optical system for separating an illumination light beam emitted by the illumination device into a plurality of color light beams is added to the constituent elements of the projector of this exemplary embodiment, and that a plurality of the electro-optical devices for modulating the color light beams separated by the color separation optical system and a projection lens for projecting light modulated by the plurality of electro-optical devices are provided in this projector, a high-resolution color display can be realized.